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United States Patent |
5,048,137
|
Rogers
|
September 17, 1991
|
Edge-shear reduction in body support foam pads
Abstract
Shear stress on the skin is relieved at cavity edges in a resilient foam
pad by cavity walls shaped to define a region of diminished support under
the cavity edge. The edge material yields more easily under loading and
may roll into the cavity to avoid pressing into body tissues. The interior
wall or walls of the cavity are slanted outwardly to undercut all or part
of the cavity edge to reduce the thickness of material under the edge. The
shape and curvature of the cavity and cavity walls can be adapted and
tailored to achieve particular pressure gradients and patterns.
Inventors:
|
Rogers; John E. (P.O. Box 1437, Blue Jay, CA 92317)
|
Appl. No.:
|
570220 |
Filed:
|
August 20, 1990 |
Current U.S. Class: |
5/731; 5/729; 5/733 |
Intern'l Class: |
A47C 027/14 |
Field of Search: |
5/461,464,468,481
|
References Cited
U.S. Patent Documents
1548728 | Aug., 1925 | Milam | 5/462.
|
2659418 | Nov., 1953 | Berman | 5/464.
|
2763013 | Sep., 1956 | Valkenburgh | 5/464.
|
2953195 | Sep., 1960 | Turck, Jr. | 5/481.
|
3885257 | May., 1975 | Rogers | 5/464.
|
4955096 | Sep., 1990 | Gilroy et al. | 5/464.
|
Primary Examiner: Trettel; Michael F.
Attorney, Agent or Firm: Epstein; Natan
Claims
What is claimed is:
1. A body support pad of resilient foamed material, said pad having a top
surface between two pad ends and two sides, a single cavity in said pad
located in a central area of said pad, said cavity opening at said top
surface for relieving pressure against the coccygeal or hip bone region of
a person supported on said top surface, said opening having an edge at
said top surface and an interior wall connected with said edge,
characterized in that at least a portion of said wall is inclined away
from the vertical to undercut said edge and define a region of diminished
support at said top surface adjacent to said edge thereby to reduce shear
stress on said anatomical portion at said edge.
2. The pad of claim 1, characterized in that said wall is shaped so that
the cross sectional dimension of said cavity in a plane parallel to said
top surface increases in a direction away from said top surface to
undercut said edge and allow said edge to roll into said cavity in
response to loading of said top surface thereby to reduce shear stress on
said anatomical portion at said edge.
3. The pad of claim 2, said cavity having a narrow end open at said top
surface for relieving pressure on a portion of the human body, said cavity
having a cavity interior of wider dimension under the open narrow end such
that pad material adjacent an edge of the open end projects into the
cavity and tends to roll into said cavity under pressure of said body to
produce a zone of graded pressure thereby on the body to relieve shear
stress on the body at said edge.
4. The body support of claim 3 wherein said pad has a bottom surface
opposite said top surface and said cavity is open at said bottom surface.
5. The pad of claim 1 wherein said pad also has a bottom surface and said
cavity is a through-hole between said top and bottom surfaces opening at
each said surface, said through-hole having a top perimeter and a bottom
perimeter respectively, said wall connecting said perimeters,
characterized in that at least a portion of said wall widens outwardly to
undercut at least a corresponding portion of said top perimeter such that
the undercut portion of said top perimeter yields to body pressure on said
top surface by rolling into said through-hole thereby to relieve the body
of shear stress at said perimeter.
6. The pad of claim 5 wherein said top perimeter is a smaller circle and
said bottom perimeter is a larger circle and said wall widens in
frustoconical shape between said perimeters.
7. The pad of claim 5 wherein said perimeters are circular and said wall
widens convexly between said perimeters.
8. The pad of claim 5 wherein said perimeters are circular and said wall
widens concavely between said perimeters.
9. The pad of claim 5, characterized in that said top perimeter is smaller
than said bottom perimeter.
10. The pad of claim 1, characterized in that at least part of said cavity
enlarges under said edge to define a ledge adapted to roll into said
cavity under body pressure bearing on said top surface and produce a zone
of graded support against the body adjacent to said edge thereby to
relieve shear stress on the body at said edge.
11. The pad of claim 1 having means defining a zone of graded resilience of
said foamed material along an uncut continuous portion of said top surface
adjacent to said edge thereby to relieve shear stress on the body at said
edge.
12. A body support pad of resilient material having a top surface for
supporting a human body, a single cavity in a coccygeal supporting region
of said pad for partially admitting a protuberant anatomical portion of a
human body supported thereon for relieving pressure on said anatomical
portion of the human body, said cavity having a rim at said top surface,
the interior of said cavity being shaped and configured for defining a
zone of graded pressure exerted against said human body by an uncut
continuous area of said top surface adjacent to said rim thereby to
relieve shear stress on the body at said rim, said graded pressure
diminishing with proximity to said rim.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to resilient pads, and the like for
supporting the human body in a seat or on a bed, and more particularly
relates to improvements in foamed material pads intended to better
distribute pressure on the skin to avoid injury and in particular to
prevent formation of decubitus ulcers, also known as bed sores.
A great deal of effort has been expended to devise and improve pads of
various types to distribute as evenly as possible the pressure exerted on
the body of a person resting thereon. The irregular shape and weight
distribution of the human anatomy causes certain portions of the body to
carry a disproportionate pressure load when the body is supported on a
plane surface, even if that surface is quite resilient. In a bed-ridden
person resting supine on a horizontal, uniform surface, areas of high
local pressure are typically found at the back of the heels, the sacrum
area, and the back of the head. In a side position, areas of peak pressure
typically occur in the hip bone or trochanter area in contact with the
supporting surface.
Protracted pressure against any portion of the skin has the effect of
diminishing or cutting off peripheral vascular flow to that area. If
impairment of blood flow to the affected area is sufficiently prolonged,
the tissues underlying the affected skin area will be starved of nutrients
and suffer progressive damage. Typically it is the underlying soft tissues
which are first damaged, until eventually the skin undergoes necrosis and
ulcerates in progressive manner, and unless the pressure on the area is
removed, such ulcers can become deep open wounds which are difficult to
treat and slow to heal.
It is known to make apertures or holes in a foam pad to accommodate and
relieve pressure against anatomical protuberances. For example, one or
more circular holes can be located on the pad to underlie the coccyx of
the patient. Other holes can be placed under the head, the heels, and
generally under any bony protrusion susceptible to ulceration or damage
during protracted confinement to bedrest or a chair. Such holes in prior
foam pads have been characterized by straight interior walls, that is,
walls which are perpendicular to the foam pad surface, regardless of the
shape of the hole opening on the pad surface. The response of the pad
surface to weight loading in the vicinity of such a straight walled hole
is influenced somewhat by the hole, since the pad material is deprived of
support at the interior wall defined by the hole. A load placed on the top
surface in the vicinity of a straight walled hole may find less support
than the same load placed at a point further removed from the hole because
in the former case the foam material is able to bulge into the hole and
thus yields more readily. At the pad surface however, the edge of the hole
remains relatively well supported and can press into the skin tissues of a
person lying thereon. Because of the relatively sharp transition in
pressure against the tissues at the edge, a straight walled opening or
cavity in the support surface of the foam pad can cause the skin and
underlying tissues to extrude into the hole. This sharp transition creates
shear stress in the skin and underlying tissues which tends to accelerate
breakdown and eventual ulceration of the tissues. What is needed therefore
is a means to reduce or eliminate shear stress in the tissues of a patient
at the edge of holes or cavities in a foam pad, so that holes and cavities
can be better used to relieve skin pressure and conform the pad surface to
anatomical protuberances and irregularities.
Still another benefit of this invention resides in improved control over
edema, the accumulation of fluid in tissues which extrude into a hole or
depression in the supporting surface. In the improvement of this
invention, the cavity edge becomes depressed and rounded when under load,
the tissues are largely prevented from extruding into the cavity thus
reducing the likelyhood of edema and consequent tissue damage.
SUMMARY OF THE INVENTION
It is the object of the present invention to reduce the shear stresses
imposed on the anatomy of the user at the edge of an opening in the
support surface of a foam pad. The present invention offers a means for
better controlling shear stress at support surface discontinuities, such
as at hole edges and transitions into surface depressions, cavities, and
such. In prior art pads shear stress control has been achieved by cutting
or slicing the surface of the foam pad at or near edges and
discontinuities. The present invention provides a means for controlling
shear stress at such discontinuities while retaining a continuous solid
volume of foam material around openings and cavities for better strength
and wear.
According to the invention here disclosed, a body support comprising a pad
of resilient material having a top surface for supporting a human body,
has an open cavity for relieving pressure on a portion of the human body,
the cavity having an edge at the top surface, the cavity being shaped and
configured so as to define a zone of graded body pressure along an uncut
continuous region of the top surface adjacent to the edge thereby to
relieve shear stress on the body at the edge. In particular, the cavity
may enlarge under the edge to define a ledge adapted to roll into the
cavity under loading by the person's body bearing on the top surface to
produce a zone of graded pressure against the body adjacent to the edge
thereby to relieve shear stress on the body at the edge. More
particularly, the cavity in the pad may have a narrow end open at the top
surface for admitting a portion of the human body such as a body
protuberance, the cavity widening under the open end such that pad
material adjacent the edge of the open end tends to roll into said cavity
under pressure of the body to relieve shear stress on the body at edge.
The cavity may be open at a bottom surface of the pad to form a
through-hole in the pad. The cavity may have a closed bottom or and open
bottom either of which is larger than the open top end of the cavity with
sloping walls connecting the open top and the bottom. The open top and the
bottom may assume a variety of shapes including circular, rectangular,
polygonal or irregular shapes, with corresponding modification to the
interior walls of the cavity. For a circular top and bottom, the interior
wall may be frustoconical. For rectangular top and bottom, the cavity
interior may have four trapezoidal walls defining a pyramidal cavity. One
or more of the interior walls or any portion thereof may be straight and
vertical, with only part of the cavity defined by sloping, angled walls.
Further, the walls may be straight in elevational cross-section, or may be
curved. The elevational curvature of the walls in turn may be either
convex or concave, and different portions of the walls may have different
curvatures to obtain tailored gradients of resilience and response to
pressure loading of the pad top surface in the vicinity of the cavity
edge.
It is understood that, while reference is made to a single opening or
cavity in the foam pad in the interest of clarity of explanation, more
than one such opening or cavity can be provided in a single pad as may be
needed or desired for any particular purpose, nor do all such opening in a
given pad be identical to each other. Different cavity configurations may
be adapted to different anatomical portions throughout a particular pad.
The term pad generally includes pads of samll size for chair use and
larger pads for bed use. These and other features and advantages of this
invention will be better understood from the following detailed
description and attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of a typical bed size pad provided with a
coccigeal relief aperture according to this invention;
FIG. 2 is an elevational cross-section taken along line 2--2 in FIG. 1
showing the tapered wall of the relief aperture;
FIG. 3 shows a typical configuration of the pad in the vicinity of the
relief aperture under load;
FIG. 4 is a side view of the pad of FIG. 1 with a person supported thereon
in supine position;
FIG. 5 is an elevational cross-section taken as in FIG. 2 showing a
variation where the relief aperture has convexly curved inner walls;
FIG. 6 is an elevational cross-section taken as in FIG. 2 showing a
variation where the relief aperture has concavely curved inner walls.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to the drawings, FIGS. 1 and 2 show a rectangular pad 10
having an upper, body supporting surface 12 extending between a head end
14, foot end 16 and two sides 18. The pad 10 is made of a resilient
synthetic foam material selected from various such foams in current use
for similar applications. In FIGS. 1 and 4 the pad 10 is shown to have an
integral head-elevating raised shelf 22, and the foot end has a sloping
surface which tapers from the top surface 12 to an edge 16. The sloping
surface 24 relieves pressure against the heels of a person P lying on the
pad 10 as shown in FIG. 4 of the drawings.
The central area of the top surface 12 has an opening 20 centered between
the sides 18 and located so as to underlie the coccigeal area of an
average individual lying in a normal supine position on the pad surface
12, as in FIG. 4. The opening 20 will also underlie the hip bone
projection of the same individual lying on his or her side and stretched
generally along the center-line of the pad between the two sides 18.
The opening 20 is to relieve pressure against the bony protrusions of the
coccyx and the hip bone of a person confined to bed rest for protracted
periods of time, to avoid breakdown and ulceration of the skin over these
bony protrusions.
The opening 20 is the top aperture of a frustoconical through-hole defined
by interior walls 30 and shown in vertical cross section in FIG. 2. The
hole 30 extends fully through the thickness of the pad 10 between the top
surface 12 and the bottom surface 26 of the pad. Both top and bottom
openings 20, 28 are circular, but the top opening 20 is substantially
smaller than the lower opening 28.
Consequently, the cross sectional dimension or area of the hole increases
from top to bottom and the interior wall 30 of the through-hole is
frustoconical. The wall 30 recedes outwardly away from the edge of the top
opening 20 with increasing depth away from the top surface 12, thereby
undercutting a circumferential zone 32 of the pad surface 12 immediately
adjacent to the edge of the top opening 20. The radial extent of the zone
32 is a function of the angle of the interior wall 30 and the pad
thickness. Because of the slope angle of the inner wall 30, the thickness
of foam material underlying the surface 12 diminishes with proximity to
the edge of the top opening 20, beginning at a point on surface 12
overlying the rim of the bottom opening 28, on the undersurface 26.
Generally, the zone 32 defines a gradient of diminishing support at the
surface 12 as a function of proximity to the opening 20.
Beginning at some point sufficiently removed from the top opening 20, the
frustoconical through-hole 30 has negligible effect and the resilience and
yielding characteristics of the foam pad are dictated by the nature of the
material and the thickness of the pad. As the edge of hole 20 is
approached, the deformation of surface 12 under load will be increasingly
influenced by the internal geometry of the through-hole 30 and the region
32 of support surface 12 surrounding the through-hole yields with
increasing ease. The lack of foam material directly underlying the hole
edge allows the foam material to roll inwardly into the hole under
loading, as illustrated in FIG. 3.
The present invention reduces shear force on skin tissues at the edge of
the hole by undermining the support available at the surface 12 in the
vicinity of the edge of the top opening 20. This diminished support is
achieved by modifying the interior geometry of the hole or cavity. In
particular this may be achieved by slanting the interior wall 30 of the
cavity or hole outwardly so as to form an acute angle, i.e., less than 90
degrees, between the wall 30 and the surface 12 at the hole edge.
FIG. 3 illustrates typical response of the support surface 12 under load
around the opening 20. The load (not illustrated) is indicated by arrows F
and is approximately evenly distributed around the opening 20 on surface
12, as might be applied by the body of a person resting on the surface 12,
particularly with an anatomical protuberance projecting into the opening
20. Such a condition is illustrated in FIG. 4 where the coccyx projection
of the person P is shown overlying the opening 20 of the cavity 30. Under
load, the circumferential region 32 of surface 12 rolls into the cavity 30
and the edge of the top opening 20 is depressed below its normal, unloaded
condition shown in dotted line in FIG. 3. The edge of opening 20 is
deprived of underlying resiliency to an extent controlled by the interior
geometry of the hole and the shear effect against any overlying anatomy is
diminished accordingly. Since the area of surface 12 immediately adjacent
to the hole 20 is pushed down more readily, there is less opportunity for
anatomical tissues to extrude into the cavity 30 at the cavity edge. The
reduced support gradient around the opening 20 allows any anatomical
protuberance and surrounding anatomy to more easily shape and depress the
surface 12 around the opening 20 into a depression to a shape generally
conforming to the anatomy with relatively low shear and extrusion at the
opening 20.
Low edge-shear openings in the pad surface 12 as just described can be
achieved with a variety of cavity geometries, some of which are shown in
FIGS. 5 and 6. The cavity 30 in FIG. 2 has straight, outwardly slanting
inner walls which, for a circular top and bottom openings will define a
frustoconical through-hole in the pad. The openings 20, 28, however, need
not be circular but may assume an arbitrary shape, with corresponding
changes in the interior wall 30. For example, square openings 20, 28 may
be employed with trapezoidal interior walls connecting corresponding sides
of the top and bottom openings, resulting in a pyramidal shaped cavity.
FIG. 5 shows a low edge-shear cavity where the interior widens at a
non-uniform rate with increasing depth so that in cross-section the inner
wall 30' is convexly curved. The rate of curvature at different depths of
the cavity can be tailored and adjusted to obtain specific characteristics
of the support gradient in the zone 32 adjacent to the top opening 20.
Thus, a convex curvature shaped as in FIG. 5 will provide an initial
drop-off in support at a point somewhat removed from the edge of the hole
20 with a lesser subsequent reduction as the edge of the hole 20 is
approached because the walls near the top, i.e., near the edge of the hole
20, more closely approach a straight, vertical wall and provide firmer
support at the hole rim. Conversely, a softer edge can be obtained by
increasing the slant of the curve away from the vertical near the edge,
i.e. a more acute angle between wall 30' and surface 12 at the hole edge.
FIG. 6 shows yet another variation where the interior cavity wall 30" is
concavely curved between the top opening 20 and bottom opening 28. The
wall deviates from the vertical most pronouncedly near the top opening 20
and then curves towards the vertical as it approaches the bottom surface
26. Consequently, the degree of support provided to the surface 12 in
region 32 diminishes rapidly as the edge of the opening 20 is approached,
producing a very soft, easily deformable zone near the opening edge, with
rapidly firmer support being encountered as the distance away from the
opening 20 increases. The curved walls 30' and 30" in FIGS. 5 and 6
respectively provide variations from a more linear gradation in support
characteristics provided by the straight sloping wall 30 of FIG. 2.
It will be understood that the invention is not limited to the particular
shapes and configurations here described or illustrated in the drawings,
and that many slopes and elevational curvatures of the cavity wall 30 can
be implemented to achieve various support gradient characteristics around
an opening 20 in the support surface 12 of the pad 10. Further, the
sloping cavity wall need not extend about the entire circumference or
perimeter of the top opening 20. For example, a half-circular portion of
the top opening 20 may be supported by a straight, vertical inner wall,
while the opposite half circle 20 may have a sloping underlying wall 30.
In a rectangular opening, two opposite sides may be associated with
slanted interior walls while the remaining two sides may be associated
with vertical cavity walls. Still other combinations of straight sloping,
concave, or convex cavity walls may be provided in a single cavity of
arbitrary shape. The dimensions of the openings are not critical and may
vary to suit their purpose. For a coccigeal opening such as illustrated in
the drawings, the top opening may be two inches in diameter and the bottom
opening may be four inches in diameter in a pad about three inches thick.
In the pad 10 several cavities 30 with top and bottom openings as shown
can be grouped in a straight line to accomodate the coccygeal region of
different sized users. Various factors, which may be experimentally
determined, will influence the dimensions of the cavity and the slope and
shape of the cavity walls. In particular, the cavity design will take into
account the resilience of the particular foam material, which are
available in a variety of hardnesses and resiliencies.
The top opening 20 may also be vanishingly small, so that the support
surface is essentially uninterrupted, but will overlie a cavity shaped as
described above, e.g., a conical cavity having a pointed apex at the
supporting surface. Such a cavity will provide generally similar benefits
to those having an open top. The surface 12 over the cavity will yield to
accomodate anatomical protrusions and will offer a pressure gradient
around the cavity which will depend on the size and shape of the cavity,
as well as on the resiliency characteristics of the foam material.
The improvement of this invention does not require that the cavity have a
bottom opening 28 at an under surface 26 of the pad 10. The bottom of the
cavity may be closed by a second layer of foam adhesively affixed to the
under surface 26 of a top pad layer. In the alternative, the cavity may be
formed so as to have a closed bottom in a single layer of foam. These and
other combinations and modifications to the present invention will become
apparent to those possessed of ordinary skill in the art in light of the
foregoing description and attached drawings which are for purposes of
illustration and explanation only and not by way of limitation of the
scope of the following claims.
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